Scientists have observed the first evidence that the Southern Ocean’s ability to absorb the major greenhouse gas, carbon dioxide, has weakened by about 15 per cent per decade since 1981.

Dr Paul Fraser, who leads research into atmospheric greenhouse gases at CSIRO Marine and Atmospheric Research, says the international team’s four-year study concludes that the weakening is due to human activities.

“The researchers found that the Southern Ocean is becoming less efficient at absorbing carbon dioxide due to an increase in wind strength over the Ocean, resulting from human-induced climate change,” Dr Fraser says.

“The increase in wind strength is due to a combination of higher levels of greenhouse gases in the atmosphere and long-term ozone depletion in the stratosphere, which previous CSIRO research has shown intensifies storms over the Southern Ocean.”

The increased winds influence the processes of mixing and upwelling in the ocean, which in turn cause an increased release of carbon dioxide into the atmosphere, reducing the net absorption of carbon dioxide into the ocean.

“Combined, the Earth’s land and ocean sinks absorb about half of all carbon dioxide emissions from human activities,” Dr Fraser says. “The Southern Ocean takes up 15 per cent of these emissions, hence a reduction in its efficiency will have serious implications for atmospheric carbon dioxide concentrations over coming decades.”